Gardening Answers Knowledgebase

Plant Answer Line Question

There are a number of trees in my neighborhood which seem to be abnormal. The branches
are changing shape, and instead of being round, they have ridges growing lengthwise along them. It makes the branches look misshapen, almost like elongated stars. It looks
unnatural, maybe like a disease. I think the trees are maples. Do you know what could be causing this?

Answer:

There are some trees and shrubs whose branches normally take the form I think you are describing, which is sometimes referred to as winged or alate. I am not aware of maples which do this, so I wonder if perhaps you were seeing sweet gum trees, or Liquidambar styraciflua. According to information from the Mathilda Mathias Botanical
Garden in Los Angeles,
"One diagnostic character is the presence of corky wings on young
stems. In some cases, wings are due to stimulation of localized
phellogens along a stem angle, as in winged euonymus (Euonymus alatus).
Wings also occur on young stems of sweet gum (Liquidambar). Longitudinal
splitting is the cause of stem wings in certain species of elm (Ulmus.)

According to
the book Plant Form: an Illustrated Guide to Flowering Plant Morphology by
Adrian Bell (Oxford University Press, 1990), these wings can be part of the way a particular plant grows. The book shows an illustration of
metamers (also called phytomers), which are repeated constructional units
(like building blocks) in the plant's development. From my unscientific
perspective, I wondered if the wings might have a leaflike photosynthetic
function. I did find an article from the Botanical Gazette from February
1889 (yes, 19th century!) by Emily Gregory which examines this issue. It seems to suggest that the corky wings on the branches may have the function of increasing branch circumference and this may provide the tree with extra protection.

Plant Answer Line Question

On the Master Gardener phone clinic today, a caller was concerned about wilted and dried leaves on his tree. This seemed to be throughout the tree, as opposed to being only at the top which might have indicated damage from the bark beetle causing Dutch elm disease.

He asked about ELMguard, which is apparently an injectable substance that increases the immune system of Camperdown elms. Do you know anything about this?

Answer:

I know that there are fungicide injections that are supposed to stave off the demise of elms which are already suffering from Dutch elm disease, but if this is not what the caller's tree suffers from, it would do little good, and might actually cause harm. He should bring samples to the Master Gardener Clinic for diagnosis as a first step.

From the description of the problem, it might be phloem necrosis (also known as elm yellows), which shows up as wilted yellow or brown leaves which drop early, and affects the whole crown of the tree. It is spread by leafhoppers.

Bacterial leaf scorch usually starts with the oldest leaves and progresses through the entire crown. Leaves are brown at the edges and have a yellow halo.

Dutch elm disease does affect Ulmus glabra 'Camperdownii.' This USDA Forest Service page describes it in detail, and compares it with the two problems I mentioned above. It also talks about the use of fungicide injections.

Excerpts:
"Foliage symptoms: Symptoms of DED begin as wilting of leaves and proceed to yellowing and browning. The pattern of symptom progression within the crown varies depending on where the fungus is introduced to the tree. If the fungus enters the tree through roots grafted to infected trees (see disease cycle section), the symptoms may begin in the lower crown on the side nearest the graft and the entire crown may be affected very rapidly. If infection begins in the upper crown, symptoms often first appear at the end of an individual branch (called "flagging") and progress downward in the crown."

"Multiple branches may be individually infected, resulting in symptom development at several locations in the crown. Symptoms begin in late spring or any time later during the growing season. However, if the tree was infected the previous year (and not detected), symptoms may first be observed in early spring. Symptoms may progress throughout the whole tree in a single season, or may take two or more years."

"Injecting elms with fungicide. Certain fungicides, when properly injected, are effective in protecting elm trees from infection via beetle transmission. This treatment is expensive and must be repeated every one to three seasons, thus it is appropriate only for high value or historically important trees. The treatment itself also may pose risks to the health of the tree."

"Eradicating Dutch elm disease from newly infected trees. If a new crown infection of DED is detected early enough, there is opportunity to save a tree through pruning, fungicide injection, or both. Eradicative treatment is not possible on trees that have become infected via root graft transmission. Pruning, which can literally eradicate the fungus from the tree by removing it, has a high probability of "saving" a newly infected tree that has less than 5% of its crown affected."

To answer your question about ELMguard, there are serious doubts about its efficacy as an elm immune booster. I did find an article, dated July 2000, from South Dakota State University Extension which states:
"Dutch elm disease is showing a very large increase in the last week or two. Several cities are now reporting a four- to eight-fold increase in the incidence of the disease. Generally when we have a wet May the problem increases for the year. According to Dutch elm disease researchers the wetter years result in the creation of a vascular system that is more susceptible to the development of the disease. We have had several calls from people wanting to use ELMguard to save their trees, particularly those already marked by the city as having the disease. ELMguard is not a fungicide but a product that is designed to increase the tree's ability to fight infection (according to the ELMguard company). It may be an excellent product and we hope to have more information on it later in the year. However the company does not recommend treatments with ELMguard at this time of year or into fall, thus homeowners should not be expect this to save their infected trees. If the city has marked a tree for Dutch elm disease the tree should be removed as soon as possible to reduce the chance of infecting nearby elm."

Plant Answer Line Question

Can the sap from an elm tree be poisonous to humans? The power company recently cut down an old elm in my garden and I brushed my hand against the stump and got a splinter.
Within about twenty minutes my hand was swollen at least twice its normal size, was very painful, quite hot to the touch and itching like crazy. I ended up in the emergency room, and had to take antibiotics, but the doctor never indicated whether the extreme reaction had anything specifically to do with the type of tree.

Answer:

We have an older book on plant-induced dermatitis, Botanical Dermatology by Mitchell and Rook (Greengrass, 1979) which includes elm among the trees which can cause "woodcutter's eczema." However, it may not be the sap of the tree itself which is the problem, but perhaps the lichens and liverworts which may be growing on the tree (some of which contain usnic acid and other substances which irritate human skin). Here is an abstract of an article which describes this:Frullania liverwort phytodermatitis

If one were to saw elm wood which was covered in lichen or liverwort, the dust could be an irritant. You may have gotten a splinter which had dust on it. I'm not a medical professional, so I couldn't say with any authority what may have happened. However, a splinter of any kind can cause inflammation, and if you happen to be especially sensitive to a particular substance, whether it is the wood or sap of the elm, or traces of dust from lichens and liverworts that were on the tree's bark when it was sawed, then there might be a connection with the severe reaction you had.

Here is a link to an article about splinters from American Family Physician (June 15, 2003).
It does mention wood splinters as a source of severe inflammatory reactions, due to the oils and resins they contain.

A chart which originally appeared in June 1990 issue of the journal American Woodturner lists different types of wood and their toxicity. Elm is included because its dust can be an eye and skin irritant.